1. Field of the Invention
The present invention relates to a process for manufacture of laminated glazing units, especially those designed as equipment for vehicles of the windshield type. It relates more particularly to laminated glazing units in which the intermediate film, which is a polymer-base material disposed between rigid substrates, generally of glass, is provided with a coating having thermal properties, especially of reflection in the infrared, thus endowing these glazing units with a highly satisfactory function of protection against solar radiation.
2. Discussion of the Background
Such configurations of glazing units are known in particular from the following patents: U.S. Pat. No. 4,639,069, U.S. Pat. No. 4,369,945, EP 0303586 and WO 90/08334, wherein there are used intermediate films generally comprising a ply of transparent polymer of the polyethylene terephthalate type (PET), provided on one of its faces with the coating which reflects in the infrared, said ply being inserted between two plies of thermoplastic polymer of the polyvinyl butyral type (PVB) before the usual assembly of this multi-layer intermediate film together with the two glass substrates is performed.
A problem specific to this type of configuration soon became apparent, however: in choosing these xe2x80x9cmulti-layer intermediate filmsxe2x80x9d, with dimensions identical to those of the glass plates, the infrared-reflecting coating was disposed flush with the edge wall of the glass plates. This coating usually comprises layers which are susceptible to deterioration, especially to oxidation, in contact with moisture. This is particularly true for metallic layers, especially of silver, which tend to corrode along their periphery, such corrosion progressively spreading over their entire surface and leading to optical defects and loss of thermal performances.
Suggestions toward solving this problem have already been made. For example, U.S. Pat. No. 5,131,967 describes a technique using the laser to margin the reflecting coating deposited on the PET, thus preventing it from occupying a flush position. This technique seems to be cumbersome, however, and it substantially lengthens the production time, since the laser must achieve ablation of the reflecting coating over a peripheral strip of non-negligible width.
Another suggestion was made in U.S. Pat. No. 5,320,893: this document teaches making a cut in the thickness of the PET ply, around the periphery thereof, so that the peripheral corrosion of the reflecting coating will be stopped from spreading by this break line. It is not certain that a simple line will be able to prevent all spreading of corrosion in this way.
The purpose of the invention is therefore new processes for manufacture of this type of glazing unit, wherein the quality of the reflecting coating is preserved in the zones of visibility, while the aforesaid disadvantages are remedied, in particular while being relatively simple to use and at the same time having great efficacy and reliability.
The primary object of the invention, therefore, is a first process for manufacture of a laminated glazing unit comprising at least two rigid substrates of the glass type assembled by an intermediate film comprising at least one ply based on a polymer or polymers provided on at least one of its faces with a thin layer or a stack of thin layers having thermal properties, especially properties of reflection in the infrared. This process includes the following stages:
a)xe2x80x94the intermediate film in xe2x80x9ccompletexe2x80x9d form or already containing at least the ply provided with the thin layer or layers is cut to dimensions essentially identical to or larger than those of at least one of the two substrates,
b)xe2x80x94the said intermediate film is incised through at least the thickness of the ply provided with the thin layer or layers, in such a way as to define, in the said ply, at least one peripheral zone localized between the incision line and the edge thereof,
c)xe2x80x94the intermediate film is assembled in xe2x80x9ccompletexe2x80x9d form between the two substrates possibly by adjoining thereto any polymer ply or plies thereof which was or were missing in case it was not previously in xe2x80x9ccompletexe2x80x9d form,
d)xe2x80x94the peripheral zone or zones is or are detached from the intermediate film by pulling them mechanically,
e)xe2x80x94the laminated glazing unit is then transformed.
Here and throughout the text hereinafter, the thin layer or layers having thermal properties, especially properties of reflection in the infrared, will be referred to as the xe2x80x9cfunctional layer or layersxe2x80x9d. Under this term, the invention also comprises one or more thin layers which may also have other properties, especially optical or electrical, in addition to or instead of thermal properties.
Within the meaning of the invention, xe2x80x9cassemblyxe2x80x9d is understood as the operation comprising correctly positioning all the elements of the laminated glazing unit correctly relative to each other before performing the operation in which they are finally unified.
Within the meaning of the invention, xe2x80x9ctransformationxe2x80x9d is understood as the unification operation, which is generally performed with application of pressure and input of heat.
Finally, the intermediate film has already been described as being complete or not complete in stage a). Within the meaning of the invention, xe2x80x9ccompletexe2x80x9d must be understood as the intermediate film already containing all the polymer plies of the final laminated glazing unit, in particular a sequence of the type PVB/PET/functional layer or layers/PET/PVB (or in other words the polymer support of the functional layer or layers already embraces the two plies of polymer of thermoplastic type that will permit assembly thereof with the rigid substrate or substrates of the window-glass type in the final glazing unit). In stage a), it may already be in complete form and contain all of these plies. However, it may also be incomplete, containing only part thereof, the remaining polymer plies then being added during assembly, while superposing them on the xe2x80x9cincompletexe2x80x9d intermediate film which has been incised according to stage b).
The xe2x80x9cincompletexe2x80x9d intermediate film on which the incision is made may therefore contain only the sequence of the type PVB/PET/functional layer or layers (or in other words the polymer support provided with the functional layer or layers alone or combined in only one of the plies of thermoplastic polymer that will permit assembly thereof with a window-glass substrate or substrates).
In general, therefore, the process according to the invention comprises stages (a) to (e).
According to a first variant, the stages are performed successively in the order in which they were listed hereinabove.
According to a second variant, the order in which these stages are performed may be modified, in particular by reversing the order of stages (c) and (d), or in other words by removing the peripheral zones of the intermediate film incised according to stage (a) before proceeding with assembly. In this way it is possible, in particularly preferred manner, to perform incision according to stage (a) of the incomplete intermediate film, especially of the type PVB/PET/functional layer or layers, then to detach the incised zones, before adjoining to the intermediate film its second PVB ply and assembling it with the two window-glass substrates. (Here and throughout the text hereinafter, the specific term PVB, which is merely an example, must be understood as any ply of thermoplastic polymer, while the specific term PET must be understood as any ply of polymer of flexible type capable of being provided with a functional layer or layers).
The process according to the invention is particularly advantageous: in fact, in the completed laminated glazing unit, the ply provided with the reflecting coating is effectively xe2x80x9cmarginedxe2x80x9d when the incision line follows its entire periphery, the margining having been performed in such a way that the reflecting coating (the functional thin layer or layers) is no longer disposed flush with the edge wall of the glass plates, thus considerably reducing and even completely eliminating the risks of corrosion via the edge walls.
The technique of the invention in fact permits xe2x80x9cselectivexe2x80x9d margining, in the sense that the form of the incision line or lines can be modulated specifically in such a way that the margining for each configuration of glazing unit is matched to the scope of corrosion risks. Thus the margining can be chosen over a more or less broad peripheral strip of the ply depending on the glazing unit. In addition, in one and the same glazing unit, the width and form of the peripheral zones which will define margining of the ply can be varied, for example in order to xe2x80x9coutlinexe2x80x9d the planned placement between substrates and ply of elements which tend to pose corrosion risks or to create weak spots in the peripheral imperviousness, for example, as will be detailed hereinafter, elements for connecting circuitry, sensors, radio antennas, or in order to allow for special geometric forms of the glazing units.
The technique according to the invention is therefore particularly flexible and permits margining which is particularly modulable geometrically and particularly precise. Thus the incision line or lines may be chosen so as to follow the form of the edge walls of the substrates very precisely, in smaller proportions, especially in such a way that the ply, once the glazing unit is completed, has the same roundings at the corners as do the substrates themselves, giving a fully esthetic impression. It is also possible to provide broader margining in the zones in which the edge walls of the glass plates have very specific forms, for example pointed forms, which may create weak points for attack by moisture.
The technique of the invention is in addition easy to use, most particularly during the assembly phase. In fact, it is easy to position the intermediate film correctly relative to the two glass plates, since the intermediate film is at least as large as those plates. (If larger, it is merely necessary to perform final clipping). It is a little more difficult to have to position an intermediate film which has already been margined and has smaller dimensions than those of the two glass plates, because in this case an almost constant distance relative to the edge walls of the glass plate must be provided all around its periphery.
Advantageously, the ply provided with the reflecting thin layer or layers is based on a flexible polymer or polymers, usually transparent or substantially transparent, especially belonging to the polyester family, of the linear polyester type, such as polyethylene terephthalate (PET), polycarbonates, polypropylene, polyethylene, polyether sulfides, polysulfides, and in general polymethacrylates. PET is particularly suitable for this application.
Preferably the intermediate film is xe2x80x9ccompositexe2x80x9d in the sense that it comprises a plurality of polymer-base plies. Advantageously it has a configuration in which the ply provided with the thin layer or layers, especially of PET, is disposed between at least two plies based on a thermoplastic polymer or polymers, which are well suited to assembly by lamination together with rigid substrates of the glass type. More particularly, the plies can be based on polyvinyl butyral (PVB) or on a polyurethane or polyurethanes (PU).
In the case of such a xe2x80x9ccompositexe2x80x9d intermediate film, when an incision is made in the ply provided with the thin layer or layers in stage (b), an incision is simultaneously made in the ply or plies topping it (and possibly to some extent in the underlying plies as well). In fact, the simplest approach is to perform this stage (b) on the complete intermediate film, once all of its constitutive plies have been assembled. Incision of plies xe2x80x9cabovexe2x80x9d the functional ply with a thin layer or layers does not pose any problem of peripheral imperviousness. In fact, during mechanical detachment of the functional ply in stage (d), especially when it comprises PET, the ply or plies associated therewith in the intermediate film, of PVB type, and which themselves may have been incised during stage (b), remain in place between the two rigid substrates: during transformation, generally using at the same time means of the suction ring type for applying peripheral vacuum, means for applying pressure on the glazing unit and heating means, in the case of a composite intermediate film of the PVB/PET/PVB type, the two PVB plies joined together in the peripheral zones where the PET ply has been removed coalesce with each other, thus creating an impervious seam relative to the edge of the PET ply provided with the thin layer or layers. Preferably, during stage (d), only the peripheral zone or zones of the ply provided with a layer or layers is or are detached. It must be noted that, in the case of an intermediate film of the PVT/PET/PVB type, the incision stage can be performed on the xe2x80x9cincompletexe2x80x9d intermediate film comprising two-ply PVB/PET, and the second ply of PVB will then be added during assembly.
The incision according to stage (b) can be performed in different ways: a cut can be provided by stamping or by a movable tool provided with a slicing element of the blade or laser type. This latter variant is more advantageous, because the movement of the movable tool can be controlled in automated manner by modifying its path and/or its cutting depth as desired, along the desired incision line or the dimensions of the laminated glazing unit to be fabricated, by simple reprogramming of the movable tool by computerized/electronic means. In particular, cutting devices of the type sold commercially by the ARISTO or Zxc3x9cND companies can be used.
As regards the choice of the layer or stack of layers designed to endow the glazing unit with thermal properties, especially reflection in the infrared, there can be chosen at least one substantially metallic layer, especially based on at least one of the following metals: silver, copper, gold, nickel, chromium, indium, tantalum, niobium, aluminum, especially an alloy of the nickel-chromium type or one belonging to the family of steels, or else one based on a metal nitride of the type TiN, ZrN or else based on doped metal oxide or oxides such as tin oxide doped with fluorine (SnO2:F) or indium oxide doped with tin (ITO). In fact, the criterion is such that the layers can be deposited on polymer substrates of PET type by known techniques.
There can be used a single layer of this type or a plurality separated by layers based on dielectric materials of the metal oxide type (Nb2O5, Ta2O5, ZnO, In2O3, TiO2, SnO2, Al2O3, WO3, etc.) or nitride of the Si3N4 type or other materials of the MgF2 type. For more information on stacks of this type, it is possible in particular to consult European Patent EP 0438357, which describes a layer based on tantalum, European Patent EP 0511901, which describes a layer based on nickel-chromium alloy, steel or tantalum associated with dielectric layers of the SnO2, TiO2, Ta2O5 type. It is also possible to consult European Patents EP 0506507, EP 0611213, EP 0636587, EP 0678484, EP 0718250 for stacks which use a layer of silver between at least two layers of dielectric material, or else European Patent EP 0638528 for stacks which use two layers of silver with a layer or layers of dielectric material interposed therebetween.
To facilitate detachment by mechanically pulling the xe2x80x9cincisedxe2x80x9d peripheral zones of the ply provided with the thin layer or layers during stage (d), it can be advantageously provided that these peripheral zones have dimensions such that they locally xe2x80x9coverhangxe2x80x9d the edge walls of the rigid substrates once the intermediate film has been positioned therebetween, especially in the form of a starting tab or tabs on which it is easy to exert mechanical pulling action to detach the said peripheral zones. To facilitate detachment, it is preferable to provide these tabs in the extension of at least one of the edges of the glass plates.
According to a particular variant of the invention, it can be provided that the thin layer or layers having thermal properties is or are provided with electricity supply means. In this way they can be endowed as desired with a heating-layer function, which is particularly useful for demisting or deicing the glazing units, especially those constituting equipment of vehicles of the windshield type, where visibility is imperative. What then remains is development of the placement of the connecting circuitry permitting them to be supplied with electricity, in such a way that the operation of detachment of the peripheral zones during stage (s) of the process of the invention does not cause damage.
According to another variant of the invention, it is also possible to provide, in one of the faces of at least one of the plies which constitutes the intermediate film and which is not in contact with the layer or layers having thermal properties, a heating layer or a network of heating wires together with their appropriate connecting circuitry. The simplest configuration, in an intermediate film of type PVB/PET/layer or layers having thermal properties/PVB, consists of providing on one of the faces of the PVB designed to be placed in contact with the rigid substrate of the glass type, a network of heating wires which is caused in known manner to become xe2x80x9cinlaidxe2x80x9d on its surface. This network, again in known manner, is supplied by oppositely disposed current leads which are sometimes called xe2x80x9cbusbarsxe2x80x9d and are made of strips of metal of the copper type. The dimensions of this network and the positioning of these xe2x80x9cbusbarsxe2x80x9d with respect to the edge of the laminated glazing unit can remain identical to the dimensions and positionings of this type of heating network of a xe2x80x9cstandardxe2x80x9d laminated unit, where the intermediate film is made merely of one thermoplastic ply of the PVB type. In fact, according to the process of the invention, only the ply of the intermediate film which is provided with the thin layer or layers having thermal properties is xe2x80x9cmarginedxe2x80x9d in the final laminated glazing unit, while the other polymer plies associated therewith, especially that of PVB, remain in place and have dimensions adjusted exactly to those of the two glass plates. Advantageously, the network of heating wires is dimensioned in such a way as to be spaced by at most 1 cm, especially about 6 to 8 mm, from the edge wall of the glass substrates of the glazing unit once it has been laminated.
The xe2x80x9cincision linexe2x80x9d in the ply provided with the layer or layers having thermal properties, which will determine the peripheral zones to be ultimately detached from the said ply, can have very varied profiles depending on the needs. Thus, in the simplest configuration, it can xe2x80x9cfollowxe2x80x9d, at least partly and in smaller proportions, a profile which is identical or close to that of the edge walls of the rigid substrates of the glass type. In this way there is achieved margining of the ply which is esthetic, regular, extremely precise and which can easily conform to and follow the xe2x80x9croundingsxe2x80x9d of the glass plates.
The said line can therefore be chosen in such a way that, once assembly has been completed, there exists, between the edge wall of the ply and the edge walls of the rigid substrates of the glass type, a margin which is always at least 3 mm, especially at least 5 mm, preferably about 6 mm. In this way there is assured sufficient distance between the edges of the thin layer or layers having thermal properties and the edges of the glazing unit itself, thus avoiding any risk of corrosion of the layer or layers via the edges.
Although the laminated glazing unit is more complex in the sense that it contains elements inserted between the glass substrates and the intermediate film, it is possible as a consequence to adapt the incision line in such a way that it xe2x80x9cenclavesxe2x80x9d the said elements: once the peripheral zones have been detached along this line, these elements will therefore be in contact with the plies of the intermediate film which are not provided with the layer or layers having thermal properties, and the ply provided with this layer or these layers has dimensions such that it xe2x80x9coutlinesxe2x80x9d them. The advantage once again is to protect the thin layer or layers in the zones where it or they would be more susceptible to corrosion attack, due to penetration of moisture, for example, especially such zones in which elements in addition to the materials specific to the laminated glazing unit are present. Such elements can include all the elements of the connecting circuitry, for example those cited hereinabove for supplying a network of heating wires, more particularly in the junction zone between the collectors (busbars) and the current leads. They can also be sensors of types such as volumetric sensors, moisture sensors, ultrasonic sensors, sensors of the type used in remote toll-charge recording. They can also be electronic elements of the electronic chip type, or wave transmitter/receiver elements of the radio antenna type.
According to one variant of the invention, it is also possible, during stage b) of incision of the intermediate film, to provide for incisions to be made along a closed line, to create xe2x80x9cwindowsxe2x80x9d in the central part, or in other words not at the periphery, of the ply provided with its thin layer or layers.
Once these xe2x80x9cwindowsxe2x80x9d have been incised, they can be manually detached from the intermediate film before the assembly stage. This internal margining makes it possible to insert diverse elements in the non-peripheral portion, especially all types of sensors, electronic elements cited hereinabove, such as remote sensors for toll-charge recording or antenna elements for systems such as the xe2x80x9cG.P.S.xe2x80x9d (a technique of identifying locations by satellite, otherwise known as xe2x80x9cGlobal Positioning Systemxe2x80x9d. It has also proved useful without adding any element in the xe2x80x9cwindowxe2x80x9d thus created, especially for use as a window which allows electromagnetic waves to pass (application to remote toll-charge recording).
According to the invention, it is possible during stage (d) to provide for masking, by means of an opacifying coating, of all or part of the zones of the intermediate film corresponding to the zones (xe2x80x9cwindowsxe2x80x9d and/or border of the ply) extracted from the ply provided with the layer or layers having thermal properties. This coating can be deposited directly on one of the faces of one of the glass substrates, especially by deposition of enamel. The deposit can be applied on the outwardly directed glass face or on the glass face designed to be located on the side next to the intermediate film, this latter type of deposit being described in particular in International Patent WO-94/22779. The opacifying coating can also be deposited by an ink-jet or silk-screen printing technique, on one of the glass plates or on one of the faces of one of the polymer-base plies associated with the ply provided with the thin layer or layers having thermal properties in the intermediate film. It can also be a deposit of opaque paint, especially one based on polyurethane. If this deposit is applied on the glass face turned toward the intermediate film, it is useful to provide a paint having good compatibility with the polymer with which it will be in contact, in order to be sure of good adherence between glass and polymer in the paint zone.
It is also possible to opacify the border of one of the PVB plies in an intermediate film of the PVB/PET/PVB type, and even to color it throughout. It is in fact advantageous to use already existing plies of the PVB type which are provided at the periphery with a strip colored throughout, especially in blues or greens, possibly with a gradation of color, especially toward the interior of the ply.
By such masking it is ensured that, once mounted, slightly clearer zones, of slightly different shade corresponding to the xe2x80x9cmarginedxe2x80x9d zones, cannot be distinguished at the periphery of the laminated glazing unit from the ply provided with the layer or layers. However, this is not indispensable at the esthetic level: in fact, the invention makes it possible to obtain a very sharp, very precise xe2x80x9ctransitionxe2x80x9d, which ultimately is esthetic in itself, which does not necessarily have to be concealed.
A particularly preferred embodiment according to the invention comprises manufacturing a laminated glazing unit made of two glass substrates assembled by a xe2x80x9cthree-layerxe2x80x9d intermediate film, of which one layer is a PET ply provided with at least one infrared-reflecting layer of the metallic type, disposed between two plies of thermoplastic polymer of the PVB type, the ply and its layer being set back from the edge walls of the two glass plates and these two thermoplastic plies acting by mutual adhesion to seal the periphery from the outside. In fact, assembly of a laminated glazing unit is generally achieved by heating and application of pressure, especially by passing the preassembled glazing unit through an autoclave: in fact, when the edges of the two PVB plies become tacky and soft, they become unified in the peripheral zone where the ply of PET type has been margined, perfectly sealing in the reflecting layer.
As mentioned hereinabove, elements of types such as elements of connection circuitry, sensors, antennas, electronic elements are inserted if desired in these xe2x80x9csetbackxe2x80x9d zones and/or in the xe2x80x9cwindowsxe2x80x9d cut in or at the edge of the ply of PET type, such elements thus being xe2x80x9cembeddedxe2x80x9d in the PVB or at the PVB/glass interface.
Another object of the invention is a process for manufacture of the same type of glazing unit, which meets the same criteria as for the preceding process and which represents a special embodiment thereof.
This second process includes the following stages:
a)xe2x80x94the intermediate film in xe2x80x9ccompletexe2x80x9d form or already containing at least the ply provided with the thin layer or layers is cut to dimensions essentially identical to or larger than those of at least one of the two substrates (stage identical to that of the first process),
b)xe2x80x94the intermediate film is incised through at least the thickness of the ply provided with the thin layer or layers, one xe2x80x9cinsidexe2x80x9d the other, in such a way as to define at least one zone between these two lines,
c)xe2x80x94at least the ply provided with the thin layer or layers is extracted from the intermediate film in this zone defined by the two incision lines,
d)xe2x80x94the intermediate film is assembled in xe2x80x9ccompletexe2x80x9d form between the two substrates by adjoining thereto any polymer ply or plies thereof which was or were missing in case it was not previously in xe2x80x9ccompletexe2x80x9d form (stage identical to stage c) of the first process),
e)xe2x80x94the laminated glazing unit is then transformed (stage identical to stage e) of the first process).
(The terminology is the same as for the preceding process).
By incision lines xe2x80x9cone inside the otherxe2x80x9d there are understood here two lines such that the inner area defined by one of the two lines is disposed completely inside the inner area defined by the other line. In fact, the PET ply of the intermediate film is not xe2x80x9cmarginedxe2x80x9d in this case, but instead there is extracted therefrom a border, a xe2x80x9ctroughxe2x80x9d at a distance close to the edge wall of the intermediate film, said border, xe2x80x9ctrough,xe2x80x9d corresponding to the zone of the ply which is located between the two incision lines and which will be extracted before assembly. This therefore does not prevent the possibility that incipient corrosion of the thin layer or layers could develop on the external periphery of the glazing unit once it has been transformed, but such incipient corrosion will be completely xe2x80x9cstoppedxe2x80x9d by this trough, which creates in the layer or layers a sufficient discontinuity that propagation of corrosion toward the central portion of the glazing unit is prevented. It may be possible to mask the periphery of the glazing unit where traces of corrosion can develop, especially by an opacifying coating such as those described in the context of the first process.
In this specific embodiment, just as in the more general process according to the invention mentioned hereinabove, it must therefore be understood that, in the final glazing unit, the integrity of the functional layer is preserved in the zone of visibility of the glazing unit, with two kinds of forms in particular:
either the layer (and its support) is truly margined, in which case the entire layer remaining in the final glazing unit is protected,
or, by virtue of the trough described hereinabove, margining does not take place, in the sense that the layer and its support are not necessarily set back from the edge walls of the glass plates of the final glazing unit, but the central zone of the layer defined by the xe2x80x9cinnermostxe2x80x9d incision line remains integrated, while the zone of the layer outside the trough, or in other words the extreme peripheral zone, is considered to be xe2x80x9csacrificedxe2x80x9d and no longer part proper of the xe2x80x9coperationalxe2x80x9d/xe2x80x9ceffectivexe2x80x9d functional layer within the meaning of the invention.
The width of the xe2x80x9ctroughxe2x80x9d can be adjusted as desired. It can assume the form of a strip of constant thickness, whose profile follows that of the edge walls of the glass plates, but in smaller proportions. It can also be of variable width, and in particular can be wider in the zones most susceptible to corrosive attack.
This trough can be extracted before assembly by manual or automated mechanical pulling action. If the incision is made not only over the thickness of the ply provided with a layer or layers of the PET type but also over the ply which covers it and which constitutes part of the intermediate film, for example of PVB, it may be preferable, once extraction has been accomplished, to add a PVB strip of suitable dimensions in the extracted zone, so that the quality of lamination does not suffer from the presence of an intermediate film which is less thick locally. This is not indispensable, however, especially when the width of the xe2x80x9ctroughxe2x80x9d is small, which is generally the case (on the order of 1 to 3 mm, for example).
Another object of the invention is a process for manufacture of the same type of glazing unit, which meets the same criteria as for the two preceding processes.
This third process includes the following stages:
axe2x80x2)xe2x80x94the intermediate film is cut to dimensions smaller than those of the two glass substrates,
bxe2x80x2)xe2x80x94the intermediate film is positioned in contact with one of the two glass substrates, in such a way that it is set back at least in part from the edge walls of the glass plates,
cxe2x80x2)xe2x80x94one or more polymer-base strips, especially of thermoplastic polymer of the PVB type, is or are disposed on the glass face turned toward the intermediate film left bare where said ply is set back,
dxe2x80x2)xe2x80x94this first glass plate provided with the intermediate film and this strip or strips is assembled together with the second glass plate, then the usual transformation to a laminated glazing unit is effected.
In this case, xe2x80x9cintermediate filmxe2x80x9d must be understood as the same structure and nature of materials as in the scope of the preceding processes (of the type PVB/PET/layer or layers/PVB).
For stage (axe2x80x2), there is chosen a size of intermediate film such that the desired margining is obtained de facto, generally in xe2x80x9cstandardxe2x80x9d forms with square corners, although it is not prohibited from having a more complex, modulated profile.
For stage (cxe2x80x2), one or more strips of thermoplastic polymer is or are used in the margined zones, and they in fact act as a sealing peripheral seam which guarantees the imperviousness of the thin layer or layers having thermal property or properties, and of the laminated glazing unit in general.
PVB-base strips are chosen which have optimal compatibility with the thermoplastic polymer plies of the intermediate film framing the ply provided with the thin layer or layers which, as has been seen hereinabove, are also usually based on PVB. The strips can have a form exactly complementary to the form of the intermediate film in order to be flush with the edge walls of the glass plates, or they can have smaller dimensions and slightly simpler form: during assembly, this strip or these strips tend in fact to flow under the effect of heat and/or pressure and in doing so fill every available interstice, while any xe2x80x9coverhangxe2x80x9d that may occur necessitates final trimming.
It is possible to attempt to achieve a maximum imperviousness effect by appropriately selecting the composition of this strip or these strips. Thus, although the base thereof may be PVB, its formulation has been optimized to reinforce its moisture-barrier properties, for example by inclusion of appropriate additives known to those skilled in the art.
This strip or these strips can be deposited either manually by an operator or by an appropriate device, especially of automated type.